In the 8 bit computer era, we knew exactly how much time any given instruction took. Retrieving some precision clock (not available!) and computing the time delta between runs - as is trivially done today - would probably be more computing power than they had at the time. Every cycle counted. Not very surprising that it wasn't done at that era. Also, there wasn't a "winning" instruction set or compilers able to target different architectures, so there was far more at stake than just clock speeds. If they changed the processor, you lost all your software.

DOS didn't have any precision clocks either as far as I know (it seems that there's interrupt 1A but it only updates 18 times a second, which is an eternity). Apparently there's 8254 based timer code after a few PC generations.

Windows 95 came up with QueryPerformanceCounter() and that simplified life quite a bit.